1. Field of the Invention
The present invention relates generally to adjusting the gain of one or more microphones based on the position and/or orientation of a speaker relative to the microphones.
2. Description of the Related Art
Audio systems, including stage systems, teleconferencing and video conferencing systems, lecture videotaping and distance learning systems, mobile telephones, and other media typically include one or more microphones for receiving a person's voice, an amplifier that amplifies the output of the microphone, and an audio speakers that plays the amplified sound. Ordinarily, when an audio system is calibrated, the volume output by the audio speaker is adjusted (by, e.g., adjusting the amplifier gain) to a desired volume for the case where a person speaks directly into the microphone. This can be thought of as calibrating the system for a 0° orientation of the person's head relative to the microphone, at a nominal mouth-to-microphone distance.
Should the speaker move away from the microphone or turn her head away from the 0° orientation, however, the sound level at the microphone is less than what the system was calibrated for. The audio speaker volume accordingly decreases, which can be annoying and distracting. On the other hand, if the system is calibrated for a head orientation of other than 0°, when the person subsequently speaks directly into the microphone the audio speaker volume increases, again potentially distracting the intended recipient or recipients from what the person is saying.
The common approach to resolving the above-noted problem is to physically hold the microphone in a single location in front of the person's mouth, either by clipping the microphone to the person's clothes, by suspending the microphone from a head-worn harness in front of the person's mouth, or by training the person to steadily hold the microphone in front of her mouth. All of these approaches suffer drawbacks. Even when a microphone is clipped to clothing, the person can turn her head away from the microphone to an orientation other than that for which the system was calibrated. Many people do not like to wear harnesses on their heads, and even experienced stage performers can temporarily wave a hand held microphone away from their mouths without intending to.
Accordingly, the present invention recognizes that it would be desirable to automatically adjust the gain of an audio system in synchronization with the head movements of a speaking person relative to a microphone. Past attempts at automatic gain adjust do not use actual speaker motion to adjust gain but instead are based on attempting to vary gain to establish a baseline audio output in response to varying received audible levels, which at best are indirectly related to speaker motion. Representative of such systems are those disclosed in U.S. Pat. Nos. 5,640,490, 5,896,450, and 4,499,578. Unfortunately, a speaker might deliberately vary her voice volume, a speaking technique that is frustrated by systems that establish amplifier gain based only on received audio signals. The present invention understands that it would be desirable to more precisely adjust audio system gain based on actual speaker movement relative to a microphone or microphones. The present invention also recognizes that conventional AGC may amplify background noise when the speaker is silent.